Developer with toner and carrier, and image forming apparatus using the same

Abstract

A developer according to an embodiment includes a toner having a color erasable by heating and a carrier. The carrier includes a core portion and a coating portion covering at least 50% of the core portion. The coating portion includes an additive agent which suppresses an increase in electrification due to friction between the toner and the carrier. The additive agent has a white color.

What is claimed is: 
     
       1. A developer for use in an image forming apparatus, the developer comprising:
 a toner having a color erasable by heating; and 
 a carrier including a core portion and a coating portion covering at least 50% of the core portion, wherein 
 the coating portion includes an additive agent which suppresses an increase in electrification due to friction between the toner and the carrier, 
 the additive agent has a white color, and 
 when an image is formed with the erasable toner on a blank sheet having an initial color space of a 0 *, b 0 * and L 0 *, and when the sheet having the erasable toner image fixed thereon is heated above a color erasing temperature, the erasable toner image has an erased color space of a*, b* and L* such that √{square root over ((a*+a 0 *) 2 +(b*+b 0 *) 2 +(L*+L 0 *) 2 )} is less than approximately 1.8. 
 
     
     
       2. The developer according to  claim 1 , wherein a mass of the additive agent included in the coating portion is between 20% and 60% of a total mass of the coating portion. 
     
     
       3. The developer according to  claim 2 , wherein the mass of the additive agent included in the coating portion is between 30% and 50% of the total mass of the coating portion. 
     
     
       4. The developer according to  claim 1 , wherein an electrical resistivity of the carrier is between 8×10 8  and 8×10 10  (Ω·cm). 
     
     
       5. The developer according to  claim 4 , wherein the electrical resistivity of the carrier is between 5×10 9  and 2×10 10  (Ω·cm). 
     
     
       6. The developer according to  claim 1 , wherein a ratio of a mass of the coating portion to a mass of the core portion is between 0.004 and 0.02. 
     
     
       7. The developer according to  claim 6 , wherein the ratio of a mass of the coating portion to the mass of the core portion is between 0.01 and 0.02. 
     
     
       8. The developer according to  claim 1 , wherein a mass of the carrier is between 90% and 93% of the total mass of the developer. 
     
     
       9. The developer according to  claim 1 , wherein a volume average particle diameter of a particle group of the carrier is between 37 μm and 43 μm. 
     
     
       10. The developer according to  claim 1 , wherein the toner includes a coloring agent and a binder resin, wherein a mass of the binder resin is between 60% and 80% of the total mass of the toner. 
     
     
       11. The developer according to  claim 1 , wherein the developer has an initial electrification of Q i (μC/g) and a saturated electrification of Q s (μC/g) such that Q s (μC/g)−Q i (μC/g) is less than approximately 18 μC/g. 
     
     
       12. A method of forming an erasable image comprising the steps of:
 forming an electrostatic image on a photoreceptor drum; 
 providing a developer to the photoreceptor drum to develop the electrostatic image into an erasable toner image; 
 transferring the erasable toner image to a blank sheet having an initial color space of a 0 *, b 0 * and L* 0 ; and 
 fixing the erasable toner image on the sheet, wherein
 the developer includes erasable toner and a carrier have a core portion and a coating portion covering at least 50% of the core portion, 
 the coating portion includes an additive agent which suppresses an excessive increase in electrification due to friction between the toner and the carrier, 
 the additive agent has a white color, and 
 when the sheet having the erasable toner image fixed thereon is heated above a color erasing temperature, the erasable toner image has an erased color space of a*, b* and L* such that √{square root over ((a*+a 0 *) 2 +(b*+b 0 *) 2 +(L*+L* 0 *) 2 )} is less than approximately 1.8. 
 
 
     
     
       13. The method according to  claim 11 , wherein the developer has an initial electrification of Q i  (μC/g) and a saturated electrification of Q s  (μC/g) such that Q s  (μC/g)−Q i  (μC/g) is less than approximately 18 μC/g.